1. Field of the Invention
This invention relates to anionic-graft polymers. More particularly, the invention relates to viscosity improving polymeric additives which also imrove the sludge dispersancy of oleaginous compositions and to the preparation of such additives. Broadly, the novel additives are polymers prepared by an anionic-graft polymerization of monomers containing at least one vinylidene group, or N,N(di C.sub.1-10 hydrocarboxyl carbodiimide group, onto an oxidized copolymer of ethylene and propylene which previously had been contacted with a strong base such as butyllithium.
2. Description of the Prior Art
The literature abounds with discussions of multifunctional viscosity index (V.I.) improvers usually containing nitrogen to enhance their dispersant activity, including polymeric nitrile-containing substances, as lubricating oil additives with detergent-dispersant and other properties.
The preparation of such multifunctional V.I. improving polymeric substances according to the prior art included: copolymerization of one or more olefins with a nitrile containing monomer (U.S. Pat. No. 3,445,387); free radical-grafting a hydroperoxidized ethylene copolymer with a polar vinylidene monomer, such as acrylonitrile (see U.S. Pat. No. 3,404,091); reacting a nitrile-containing compound with a reactive copolymer such as is obtained from free radical-grafting of maleic anhydride to polyisobutylene (see U.S. Pat. No. 3,448,049); free radical-grafting an ester of an aminoalcohol onto an oxidized interpolymer of ethylene and propylene (see U.S. Pat. No. 3,687,849); and, thermally reacting amines with an oxidized ethylene-propylene copolymer (see U.S. Pat. No. 3,864,268).
These processes which utilize free radicals have certain disadvantages, including irreversible crosslinking of the copolymer and homopolymerization of monomeric components. One of such disadvantages is shown by U.S. Pat. No. 3,236,917 wherein the initiation of the desired addition reaction by the generation of free radicals also provokes grafting of a single molecule of maleic anhydride into two copolymer chains thereby irreversibly crosslinking the copolymer and markedly decreasing its solubility in oil. One approach to overcoming this disadvantage is shown in U.S. Pat. No. 3,378,492 which teaches grafting an unsaturated hydrocarbon polymeric compound, e.g. polybutadiene, directly with an unsaturated, polar, nitrogen-containing organic compound, e.g. acrylonitrile, by a free radical initiated reaction.
Another approach to preparing an oil-soluble nitrogeneous ashless dispersant involves reacting an alkali metal salt of a long-chain ketone with acrylonitrile (see U.S. Pat. No. 3,565,803 and 3,723,501). Unfortunately, formation of the dialkyl ketone precursor is by ozonization which is an expensive and hazardous process involving dimethyl sulfide, an environmentally toxic agent.
Also taught as a multifunctional additive for lubricating oils is the anionic-graft polymer of a lithiated ethylene-propylene-hexadiene terpolymer with an amino methacrylate monomer (see U.S. Pat. No. 3,879,304).